This application outlines a study on intrinsic neuroregulatory mechanisms of cells which produce endogenous opiate and related peptides. The major hypothesis to be tested is that specific inhibitory and stimulatory mechanisms exist which regulate secretion of opiomelanocortin peptides. To examine the hypothesis of whether inhibition or stimulation of peptide secretion occurs directly on opiomelanocortin cells, specific neurotransmitters and neurotoxins, narcotic antagonist drugs, and selected opiate or hypothalamic peptides will be used in rodent pituitary glands in vitro. Since inhibition or stimulation of peptide secretion may also be affected by central nervous system mechanisms, an intact in vivo rodent animal model, will be treated with the same neurotoxins or narcotic antagonists as the in vitro studies. To measure the level of output of peptides from either the in vitro or in vivo systems, bioassay or radioimmunoassay for melanocyte-stimulating hormone, or radioimmunoassay for beta-endorphin, will be used. Specific effects of neurotoxins in vivo will be confirmed by high pressure liquid chromatographic (HPLC) analysis of pituitary and brain neurotransmitters. Radioimmunoassay for pituitary tissue levels of beta-endorphin will be performed in order to compare stored levels of peptide with released material in serum. Finally, cytologic and immunohistochemical studies of opiomelanocortin cells, using qualitative and quantitative methods for evaluation, will be performed within the same experimental groups as those assayed for peptides, to determine how individual groups of pituitary secretory cells respond to inhibition or stimulation. It is anticipated that neurotoxic agents or opiate antagonist drugs may have direct effects on stimulation or prevention of pituitary peptide secretion, depending upon the agents' selectivity for a particular neurotransmitter. The use of in vitro and in vivo studies on the rodent pituitary gland model, will provide support for specific mechanisms which affect release and storage of endogenous opiate molecules.